GB2302045A

GB2302045A - Pump for blood treatment; pressure sensor

Info

Publication number: GB2302045A
Application number: GB9511798A
Authority: GB
Inventors: Calvin John Ryan; Terence Gourlay
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-06-09
Filing date: 1995-06-09
Publication date: 1997-01-08
Also published as: GB9511798D0

Abstract

In a plasma apheresis or renal dialysis unit the blood is pumped by a mechanism having a flexible conduit 30 in which are located non-return valves 31. A linear actuator 33 periodically compresses a part of the tube between the valves under the control of a microprocessor. As described, a stepping motor 38 drives screw a 36 mounted in block 37 to reciprocate head 33 between guides 39 at a pulse rate of 3.33-0.833 Hz to give a volume displacement of 0.25-4 ml per stroke. A pressure sensor is described comprising a C- shaped resin clip, adapted to surround the conduit, and in which is embedded a wire acting as a strain gauge whose resistance is monitored to determine pressure.

Description

DESCRIPTION OF INVENTION "IMPROVEMENTS IN OR RELATING TO AN APHERESIS UNIT" THE PRESENT INVENTION relates to an apheresis unit and more particularly to an apheresis unit intended for use with blood.

An apheresis unit is a unit which is frequently used to extract, from blood, a component of the blood. An apheresis unit may comprise a plasma apheresis unit adapted to remove plasma from blood. The plasma removed from the blood of a particular person may, after it has been separated from the blood, be used in many different ways.

The plasma may, for example, be "donated" and used in the treatment of another patient. Alternatively, the plasma may be stored, to be returned to the person from whom the blood is taken, for example when that person is undergoing a subsequent operation. Alteratively, the plasma may be treated in some way, to remove an undesirable component from the plasma, before the plasma is re-mixed with the remaining components of the blood to be returned immediately to the patient from whom the blood was initially extracted.

Another type of apheresis unit is a renal dialysis unit. Such a unit simulates the action of the kidneys, removing from the blood water and waste products such as urea.

A problem that has been encountered with present apheresis units is the speed at which the units operate.

There are certain constraints, however, in that patients find it uncomfortable if the rate at which blood is extracted from them is increased beyond a certain limit.

However, it would be desirable if, without exceeding this blood flow rate, an apheresis unit could be provided which performs the necessary separation in a minimum period of time. It has been found that the risk of infection occurring in a patient is related to the time that the patient is connected to the apheresis unit. In other words, the longer that the patient is connected to the apheresis unit the greater chance of infection occurring.

Also, the cost of treatment is, effectively proportional to the time that a patient is connected to the apheresis unit.

A further factor is that the number of patients that can be treated by an apheresis unit is inversely proportional to the time that each patient is connected to the unit.

The present invention seeks to provide an improved apheresis unit.

According to one aspect of this invention there is provided an apheresis unit having means to receive blood from a patient, a blood treatment vessel comprising means to separate, from the blood, a predetermined component or means to treat the blood, and a transport mechanism adapted to transport fluid within the unit, the transport mechanism comprising a flexible conduit to contain the fluid provided with non-return valves at spaced apart positions, and a linear actuator adapted to compress part of the pipe between the non-return valves in a pre-selected or controllable manner.

Preferably the linear actuator comprises a stepping motor driving a lead screw which engages a ball screw nut and head mounted on the ball screw nut such that rotary motion of the stepping motor causes linear motion of the head.

Conveniently the stepping motor is adjustably controlled to provide a predetermined frequency of movement of the head and a predetermined extent of movement of the head, the transport unit thus pumping fluid in pulses of a predetermined frequency and of a predetermined volume.

In one embodiment of the invention the transport unit is connected in a line between the means to receive blood and the means to separate blood.

In an alternative embodiment of the invention the transport unit is connected in a line which receives said predetermined component from the separation chamber and supplies that component to a treatment column.

In one embodiment of the invention the separation chamber contains a semi-permeable membrane. Preferably the semi-permeable membrane is made of a polyvinyl chloride derivative.

In an alternative embodiment of the invention the separation chamber contains hollow fibres. The hollow fibres may be made of polypropylene or of cellulose diacetate.

Conveniently the transport mechanism is controlled in response to pressure measured by at leat one pressure sensor.

Preferably pressure sensor for sensing pressure within a flexible pipe, the pressure sensor comprising a clip adapted to at least partially surround the pipe or conduit, the clip being formed of a moulded material and having embedded therein at least one strain gauge.

Conveniently the sensor comprises a clip moulded of a resin material.

Conveniently the strain gauge is connected to a circuit adapted to determine the resistance of the strain gauge.

According to another aspect of this invention there is provided a pressure sensor for sensing pressure within a flexible pipe, the pressure sensor comprising a clip adapted to at least partially surround the pipe or conduit, the clip being formed of a moulded material and having embedded therein at least one strain gauge.

Preferably the sensor comprises a clip moulded of a resin material.

It is often necessary to measure the pressure of fluid present within a flexible pipe. The present invention, in another aspect, seeks to provide an improved pressure measuring device.

In order that the invention may be more readily understood and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which FIGURE 1 is a diagrammatic view of an apheresis unit incorporating the invention, FIGURE 2 is a side view of a transport mechanism or pump forming part of the arrangement illustrated in Figure 1, FIGURE 3 is a perspective view, with parts cut away, of the transport mechanism of Figure 2, and FIGURE 4 is a perspective view of a pressure sensor.

Referring initially to Figure 1, the illustrated apheresis unit is a plasma apheresis unit. The unit has an inlet 1 adapted to be connected by an appropriate connector to a patient so that blood from the patient can flow, as indicated by the arrow 2, into the unit. The blood flows through a pipe or conduit 3. A supplementary pump 4 is provided which pumps, into the pipe or conduit 3 an anticoagulant, which is admixed with the blood.

The conduit 3 is connected to a transport mechanism 5 which will be described hereinafter in greater detail. The transport mechanism provides a pulsed flow at a relatively high pressure. The frequency and the pressure of the pulsed flow can be controlled.

An outlet conduit 6 from the transport mechanism 5 passes a pressure sensor 7 and then enters a separation vessel 8. The separation vessel 8 is a vessel containing appropriate elements to separate plasma from the flow of blood. The separation vessel 8 thus has two outlets, one for a flow of plasma-reduced blood and the other for a flow of plasma. The vessel 8 may contain a semi-permeable membrane, such as a membrane made of polyvinyl chloride derivative, but typically the vessel contains a plurality of hollow fibres made of a material such as cellulose diacetate.

A first outlet 9 from the separation vessel, for the flow of plasma-reduced blood, is provided with a pressure sensor 10 and flows to a drip chamber 11. The outlet 12 of the drip chamber 11 is connected to a supplementary pump 13 which pumps the plasma-reduced blood through a line 14 to a connector 15 which is connected to the patient so that the plasma-reduced blood can flow, as indicated by the arrow 16 back into the patient.

A second outlet 17 from the separation vessel 8 is for a flow of plasma. The outlet 17 is connected to a transport mechanism 18 of the type which will be described hereinafter, the transport mechanism 18 providing a pulsed flow to an output 19 which is connected to a treatment column 20. The treatment column 20 may contain an appropriate material through which the plasma flows, the material being selected to treat the plasma, for example by removing specific toxins from the plasma.

The outlet 21 from the column 20 may pass to an appropriate reservoir if the plasma is to be stored for future use, or may be returned to the line 14 to be reintroduced into the patient from whom the blood was initially extracted in the first place.

The pressure sensors 7 and 10 are connected to a control device 22, such as a microprocessor, which controls the transport mechanisms 5 and 18.

Turning now to Figures 2 and 3 a transport mechanism, such as the transport mechanism 5 or the transport mechanism 18 is illustrated.

The transport mechanism comprises a flexible tube 30 that is connected between the inlet to the transport mechanism and the outlet from the transport mechanism. Each end of the tube 30 is provided with a nonreturn valve such as the non-return valves 31 visible in Figures 2 or 3. The tube 30 is a flexible tube preferably being formed of a silicone or silastic material. The tube 30 is located against a fixed surface 32 that forms part of a support. An actuator head 33 is located in contact with the tube 30 and is adapted to be moved linearly towards and away from the surface 32 as indicated by the arrow 34. The actuator head 33 has a substantial extent parallel to the axis of the tube, and thus a substantial length of the tube 30, between the non-return valves 31 is trapped between the head 33 and the fixed surface 32.The head is connected to a ball screw nut 35 which is mounted on a lead screw 36, the screw which passes through a support block 37 and which is driven by a stepper motor 38.

The stepper motor 38 can be controlled in such a way that the head 33 executes a linear motion in a desired manner, thus compressing the resilient pipe 30. The head 33 is guided by the linear bearings 39. As the pipe 30 is compressed, fluid present in the pipe will pass through the outlet non-return valve 31. When the pipe 30 is relaxed, it returns to its original shape and more fluid is drawn into the pipe 30 through the inlet non-return valve 31.

In a preferred embodiment of the invention the stepper motor is a Portescap stepper motor part number P532-2580.7 and has an associated Portescap stepper motor drive part number EDB-106. The ball screw, lead screw and the nut is an RHP part number WE0601MS-lY-C3Tl.

The support unit is an RHP unit part number WBK0611.

It is to be appreciated that the stepper motor may be activated to cause the head 33 to move at a selected pulse rate. It is preferred that the pulse rate is between 3.33 Hz and 0.833 Hz. The volumetric displacement can be selected by determining the degree of displacement of the head 33. The volumetric displacement on each cycle of the pump is preferably within the range of 0.25 to 4.00 ml.

It is to be appreciated that the transport mechanism as illustrated in Figures 2 and 3 will be controlled to have a selected frequency of operation and a selected displacement of the head, thus controlling the quantity of fluid pumped and the outlet pressure of the fluid that is pumped. A relatively high pressure can be obtained, and it has been found that this assists in the separation process being carried out in the separation vessel 8. Care must taken, however, to prevent the pressure exceeding a predetermined limit, since otherwise haemolysis can occur, with the red blood cells being broken.

The speed of movement of the head 33 can be controlled thus enabling each pulse of fluid pumped by the transport mechanism to have a controlled pressure or flowrate profile.

The transport unit 18 is operated to ensure that the plasma that is supplied to the column 20 is supplied at such a flow rate and such a pressure that the material within the column 20 is not disturbed in a non-uniform manner. It has been found that under certain substantially constant flow conditions of a fluid through a column, the fluid can disturb the material present in the column and form direct flow channels through the column. This means that fluid flows through the column without coming into effective contact the material in the column, substantially reducing the efficiency of the column. However, a transport mechanism of the type described with reference to Figure 2 can be controlled so that the flow of fluid through the column 20 is optimised.The flow rate may be low enough not to disturb the material in the column, or may e selected to disturb the material substantially, so that a fluidised bed of material is created in the column, leading to intimate contact between the material in the column and the fluid being pumped through the column.

Returning to Figure 1, pressure sensors 7 and 10 are identified. A typical pressure sensor is illustrated in Figure 4.

The pressure sensor of Figure 4 is intended for use in measuring the pressure present within a flexible pipe.

The pressure sensor comprises a "C" -shaped clip 40 adapted to substantially surround a pipe or conduit, the clip 40 being moulded from an appropriate resin. Embedded within the resin forming the clip is at least one strain gauge 41.

A strain gauge is a wire having a resistance which is proportional to the length of the wire. As a strain is applied to the wire, increasing the length of the wire, so the resistance of the wire will change. The strain gauge is connected to an appropriate monitoring circuit 42. The circuit 42 may be connected to, or form part of, the control device 22.

It is to be appreciated that the arrangement illustrated in Figure 1 will be controlled by the control microprocessor 22 which controls the operation of the transport mechanism, although manual controls may be provided to enable an operator to select the desired mode of operation of the arrangement.

It has been found that an apparatus as described may be used to provide a pulsatile flow, whilst controlling the pressure, and thus flow rate, within each pulse of the flow. Thus the head 33 may be moved so that a desired pressure profile is generated during each pulse. This may create turbulence within the chamber 8, enhancing the exchange mechanisms. The surface of the blood contacting the membrane or the filter hollow fibres is thus constantly changing, and the membrane or filter fibres are "cleaned".

It has been found that an arrangement in accordance with the invention may shorten the time that a patient needs to be connected to an apheresis unit by up to 40%.

This provides a double advantage. The first advantage is that because each patient is connected to the apheresis unit for a shorter period of time, there is a much less risk of infection developing in any particular patient.

The second advantage is that 40% more patients can be treated within a given period of time using the same piece of apparatus. This optimises the benefit obtained from the capital investment.

Whilst the invention has been described with reference to a plasma apheresis unit, it is to be appreciated that the invention applies equally to other types of apheresis unit, such as a renal dialysis unit, or an apheresis unit of the type in which whole blood is supplied to a separation vessel which contains an absorbent material, to separate a predetermined component from the blood by absorption, or a bio-reactive material which treats the blood.

Claims

CLAIMS:

1. An apheresis unit having means to receive blood from a patient, a blood treatment vessel comprising means to separate, from the blood, a predetermined component or means to treat the blood, and a transport mechanism adapted to transport fluid within the unit, the transport mechanism comprising a flexible conduit to contain the fluid provided with non-return valves at spaced apart positions, and a linear actuator adapted to compress part of the pipe between the non-return valves in a pre-selected or controllable manner.

2. A unit according to Claim 1 wherein the linear actuator comprises a stepping motor driving a lead screw which engages a ball screw nut and head mounted on the ball screw nut such that rotary motion of the stepping motor causes linear motion of the head.

3. A unit according to Claim 2 wherein the stepping motor is adjustably controlled to provide a predetermined frequency of movement of the head and a predetermined extent of movement of the head, the transport unit thus pumping fluid in pulses of a predetermined frequency and of a predetermined volume.

4. A unit according to Claim 3 wherein the stepping motor is adjustably controlled to provide a predetermined speed of movement of the head.

5. A unit according to any one of the preceding Claims wherein the transport unit is connected in a line between the means to receive blood and the means to separate blood.

6. A unit according to any one of Claims 1 to 4 wherein the transport unit is connected in a line which receives said predetermined component from the separation chamber and supplies that component to a treatment column.

7. A unit according to any one of the preceding Claims wherein the separation chamber contains a semi-permeable membrane.

8. A unit according to Claim 7 wherein the semipermeable membrane is made of a polyvinyl chloride derivative.

9. A unit according to any one of Claims 1 to 6 wherein the separation chamber contains hollow fibres.

10. A unit according to Claim 9 wherein the hollow fibres are made of polypropylene.

11. A unit according to Claim 9 wherein the hollow fibres are made of cellulose diacetate.

12. A unit according to any one of the preceding Claims wherein the transport mechanism is controlled in response to pressure measured by at least one pressure sensor.

13. A unit according to Claim 12 wherein the pressure sensor is a pressure sensor for sensing pressure within a flexible pipe, the pressure sensor comprising a clip adapted to at least partially surround the pipe or conduit, the clip being formed of a moulded material and having embedded therein at least one strain gauge.

14. A unit according to Claim 13 wherein the sensor comprises a clip moulded of a resin material.

15. A unit according to Claim 13 or 14 wherein the strain gauge is connected to a circuit adapted to determine the resistance of the strain gauge.

16. A pressure sensor for sensing pressure within a flexible pipe, the pressure sensor comprising a clip adapted to at least partially surround the pipe or conduit, the clip being formed of a moulded material and having embedded therein at least one strain gauge.

17. A pressure sensor according to Claim 16 wherein the sensor comprises a clip moulded of a resin material.

18. A pressure sensor according to Claim 16 or 17 wherein the strain gauge is connected to a circuit adapted to determine the resistance of the strain gauge.

19. An apheresis unit substantially as herein described with reference to and as shown in the accompanying drawings.

20. A pressure sensor substantially as herein described with reference to and as shown in Figure 4 of the accompanying drawings.

21. Any novel feature or combination of features disclosed herein.